A virus similar to measles in humans may be responsible for the deaths of more than 333 bottlenose dolphins along the East Coast this summer, researchers said Tuesday.

The morbillivirus outbreak extends from coastal areas of New York to North Carolina, causing dolphin deaths in numbers not seen since a similar fatal outbreak on the Eastern Seaboard 26 years ago.

Since July 1, researchers have found 333 dead dolphins on or near shore. Of those deaths, 174 were in Virginia, the National Oceanic and Atmospheric Administration said Tuesday. Generally, scientists find about 33 stranded bottlenose dolphins a year.

The virus likely will continue killing dolphins as long as there are susceptible animals that can be infected, said Teri Rowles of the NOAA Fisheries Marine Mammal Health and Stranding Response Program.

“We don’t have a lot of insight into when it will stop,” she said.

There’s no practical way to immunize wild dolphins, so there’s little federal wildlife officials can do about the outbreak other than to monitor it and try to figure out why it’s happening and what may have caused it.

Based on the behavior of the 1987 outbreak, researchers suspect the virus will spread south as the bottlenose dolphins head to warmer waters for the winter. It likely will last until it has killed off all but those dolphins that have developed an immunity to the virus, said Jerry Saliki of the University of Georgia.

The 1980s outbreak killed 742 dolphins; it wasn’t until several years later that researchers determined what killed them. Scientists used tools developed in a dolphin die-off in the Mediterranean to help determine what killed the bottlenose dolphins in the 1980s.

Researchers are looking at what could have caused the latest outbreak among bottlenose dolphins. Such outbreaks are common in other animal populations, scientists said, although the virus doesn’t jump from species that aren’t closely related. Humans can’t get the dolphin form of the virus, for example. But researchers have traced morbillivirus outbreaks in African lions to unvaccinated domestic dogs. And primates also get measles, Saliki said.

Because they’re looking at migratory stocks, scientists are working under a hypothesis that the dolphins that summer off the Virginia and North Carolina coasts move south in the winter, said Lance Garrison of the NOAA Southeast Fisheries Science Center.

“So one of the things that we’ll need to evaluate – if strandings are elevated along the southeast coast during the winter months – is whether that’s simply because the southern migratory stock is moving into those waters and then stranding,” he said, or whether the dolphins are catching the virus from other animals in the south.The team working on the outbreak is trying to find the first dolphin deaths, which began in February and March. They hope to be able to identify how those dolphins got sick, Rowles said. They’ll look for environmental drivers and try to determine how the virus got introduced into the bottlenose population.

They’ll also be looking at whether changing climate patterns have any role. Researchers will look at whether the disease is more likely to spread because dolphins and other marine mammals are encountering exposed populations as their territories change.